How to use SD/MMC cards with Atmel SoCs having MCI hardware
-----------------------------------------------------------
2010-08-16 Reinhard Meyer <reinhard.meyer@emk-elektronik.de>

This is a new approach to use Atmel MCI hardware with the
general MMC framework. Therefore it benefits from that
framework's abilities to handle SDHC Cards and the ability
to write blocks.

- AT91SAM9XE512 (tested, will definitely work with XE128 and XE256)
- AT91SAM9260 (not tested, but MCI is to AT91SAM9XE)
- AT91SAM9G20 (not tested, should work)

It should work with all other ATMEL devices that have MCI,
including AVR32.

The generic driver does NOT assign port pins to the MCI block
nor does it start the MCI clock. This has to be handled in a
board/SoC specific manner before the driver is initialized:

example: this is added to at91sam9260_devices.c:

#if defined(CONFIG_ATMEL_MCI) || defined(CONFIG_GENERIC_ATMEL_MCI)
void at91_mci_hw_init(void)
{
	at91_set_a_periph(AT91_PIO_PORTA, 8, PUP);	/* MCCK */
#if defined(CONFIG_ATMEL_MCI_PORTB)
	at91_set_b_periph(AT91_PIO_PORTA, 1, PUP);	/* MCCDB */
	at91_set_b_periph(AT91_PIO_PORTA, 0, PUP);	/* MCDB0 */
	at91_set_b_periph(AT91_PIO_PORTA, 5, PUP);	/* MCDB1 */
	at91_set_b_periph(AT91_PIO_PORTA, 4, PUP);	/* MCDB2 */
	at91_set_b_periph(AT91_PIO_PORTA, 3, PUP);	/* MCDB3 */
#else
	at91_set_a_periph(AT91_PIO_PORTA, 7, PUP);	/* MCCDA */
	at91_set_a_periph(AT91_PIO_PORTA, 6, PUP);	/* MCDA0 */
	at91_set_a_periph(AT91_PIO_PORTA, 9, PUP);	/* MCDA1 */
	at91_set_a_periph(AT91_PIO_PORTA, 10, PUP);	/* MCDA2 */
	at91_set_a_periph(AT91_PIO_PORTA, 11, PUP);	/* MCDA3 */
#endif
}
#endif

the board specific file need added:
...
#ifdef CONFIG_GENERIC_ATMEL_MCI
# include <mmc.h>
#endif
...
#ifdef CONFIG_GENERIC_ATMEL_MCI
/* this is a weak define that we are overriding */
int board_mmc_init(bd_t *bd)
{
	/* Enable clock */
	at91_sys_write(AT91_PMC_PCER, 1 << AT91SAM9260_ID_MCI);
	at91_mci_hw_init();

	/* This calls the atmel_mci_init in gen_atmel_mci.c */
	return atmel_mci_init((void *)AT91_BASE_MCI);
}

/* this is a weak define that we are overriding */
int board_mmc_getcd(u8 *cd, struct mmc *mmc)
{
	/*
	 * the only currently existing use of this function
	 * (fsl_esdhc.c) suggests this function must return
	 * *cs = TRUE if a card is NOT detected -> in most
	 * cases the value of the pin when the detect switch
	 * closes to GND
	 */
	*cd = at91_get_gpio_value (CONFIG_SYS_MMC_CD_PIN) ? 1 : 0;
	return 0;
}

#endif

and the board definition files needs:

/* SD/MMC card */
#define CONFIG_MMC			1
#define CONFIG_GENERIC_MMC		1
#define CONFIG_GENERIC_ATMEL_MCI	1
#define CONFIG_ATMEL_MCI_PORTB		1	/* Atmel XE-EK uses port B */
#define CONFIG_SYS_MMC_CD_PIN		AT91_PIN_PC9
#define CONFIG_CMD_MMC			1